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 $155.61   10.470%   $171.9024   $171.90   $171.90   $171.90  
  Purchase #2 $60.42   9.541%   $66.1847   $66.18   $66.20   $66.20  
  Purchase #3 $102.34   8.748%   $111.2927   $111.29   $111.30   $111.30  
  Purchase #4 $229.35   7.391%   $246.3013   $246.30   $246.30   $246.30  
  Purchase #5 $51.52   13.231%   $58.3366   $58.34   $58.35   $58.30  
  Purchase #6 $134.67   5.221%   $141.7011   $141.70   $141.70   $141.70  
  Purchase #7 $208.55   10.376%   $230.1891   $230.19   $230.20   $230.20  
  7 purchase totals = $942.46       $1,025.9079   $1,025.90   $1,025.95   $1,025.90