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 $58.29   5.237%   $61.3426   $61.34   $61.35   $61.30  
  Purchase #2 $190.34   6.818%   $203.3174   $203.32   $203.30   $203.30  
  Purchase #3 $79.88   7.526%   $85.8918   $85.89   $85.90   $85.90  
  Purchase #4 $148.76   8.430%   $161.3005   $161.30   $161.30   $161.30  
  Purchase #5 $133.90   4.194%   $139.5158   $139.52   $139.50   $139.50  
  Purchase #6 $12.29   9.503%   $13.4579   $13.46   $13.45   $13.50  
  Purchase #7 $229.68   7.188%   $246.1894   $246.19   $246.20   $246.20  
  7 purchase totals = $853.14       $911.0154   $911.02   $911.00   $911.00