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 $62.27   10.754%   $68.9665   $68.97   $68.95   $69.00  
  Purchase #2 $199.37   3.110%   $205.5704   $205.57   $205.55   $205.60  
  Purchase #3 $187.42   12.695%   $211.213   $211.21   $211.20   $211.20  
  Purchase #4 $90.72   11.137%   $100.8235   $100.82   $100.80   $100.80  
  Purchase #5 $240.46   13.502%   $272.9269   $272.93   $272.95   $272.90  
  Purchase #6 $24.88   6.845%   $26.583   $26.58   $26.60   $26.60  
  Purchase #7 $5.40   6.497%   $5.7508   $5.75   $5.75   $5.80  
  7 purchase totals = $810.52       $891.8341   $891.83   $891.80   $891.90