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 $87.26   7.248%   $93.5846   $93.58   $93.60   $93.60  
  Purchase #2 $17.67   12.111%   $19.81   $19.81   $19.80   $19.80  
  Purchase #3 $207.88   9.661%   $227.9633   $227.96   $227.95   $228.00  
  Purchase #4 $204.52   9.241%   $223.4197   $223.42   $223.40   $223.40  
  Purchase #5 $69.49   7.585%   $74.7608   $74.76   $74.75   $74.80  
  Purchase #6 $130.98   7.614%   $140.9528   $140.95   $140.95   $141.00  
  Purchase #7 $240.50   13.254%   $272.3759   $272.38   $272.40   $272.40  
  7 purchase totals = $958.30       $1,052.8671   $1,052.86   $1,052.85   $1,053.00