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 $84.90   7.325%   $91.1189   $91.12   $91.10   $91.10  
  Purchase #2 $44.79   7.640%   $48.212   $48.21   $48.20   $48.20  
  Purchase #3 $93.44   12.804%   $105.4041   $105.40   $105.40   $105.40  
  Purchase #4 $29.49   6.278%   $31.3414   $31.34   $31.35   $31.30  
  Purchase #5 $15.42   13.731%   $17.5373   $17.54   $17.55   $17.50  
  Purchase #6 $107.94   3.505%   $111.7233   $111.72   $111.70   $111.70  
  Purchase #7 $170.37   5.256%   $179.3246   $179.32   $179.30   $179.30  
  7 purchase totals = $546.35       $584.6616   $584.65   $584.60   $584.50