Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.52   8.185%   $266.6977   $266.70   $266.70   $266.70  
  Purchase #2 $172.31   5.254%   $181.3632   $181.36   $181.35   $181.40  
  Purchase #3 $195.50   7.264%   $209.7011   $209.70   $209.70   $209.70  
  Purchase #4 $156.46   13.847%   $178.125   $178.13   $178.15   $178.10  
  Purchase #5 $240.69   12.766%   $271.4165   $271.42   $271.40   $271.40  
  Purchase #6 $119.74   5.792%   $126.6753   $126.68   $126.70   $126.70  
  Purchase #7 $187.31   10.865%   $207.6612   $207.66   $207.65   $207.70  
  7 purchase totals = $1,318.53       $1,441.6400   $1,441.65   $1,441.65   $1,441.70