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 $202.77   6.366%   $215.6783   $215.68   $215.70   $215.70  
  Purchase #2 $183.36   6.263%   $194.8438   $194.84   $194.85   $194.80  
  Purchase #3 $42.56   7.283%   $45.6596   $45.66   $45.65   $45.70  
  Purchase #4 $16.84   10.870%   $18.6705   $18.67   $18.65   $18.70  
  Purchase #5 $104.60   13.763%   $118.9961   $119.00   $119.00   $119.00  
  Purchase #6 $174.92   9.393%   $191.3502   $191.35   $191.35   $191.40  
  Purchase #7 $244.33   9.571%   $267.7148   $267.71   $267.70   $267.70  
  7 purchase totals = $969.38       $1,052.9133   $1,052.91   $1,052.90   $1,053.00