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 $226.79   11.810%   $253.5739   $253.57   $253.55   $253.60  
  Purchase #2 $6.82   3.470%   $7.0567   $7.06   $7.05   $7.10  
  Purchase #3 $81.41   3.533%   $84.2862   $84.29   $84.30   $84.30  
  Purchase #4 $102.60   3.361%   $106.0484   $106.05   $106.05   $106.00  
  Purchase #5 $201.34   13.533%   $228.5873   $228.59   $228.60   $228.60  
  Purchase #6 $226.38   4.667%   $236.9452   $236.95   $236.95   $236.90  
  Purchase #7 $130.90   9.395%   $143.1981   $143.20   $143.20   $143.20  
  7 purchase totals = $976.24       $1,059.6958   $1,059.71   $1,059.70   $1,059.70