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 $250.76   5.329%   $264.123   $264.12   $264.10   $264.10  
  Purchase #2 $122.45   13.193%   $138.6048   $138.60   $138.60   $138.60  
  Purchase #3 $105.58   4.738%   $110.5824   $110.58   $110.60   $110.60  
  Purchase #4 $106.55   11.323%   $118.6147   $118.61   $118.60   $118.60  
  Purchase #5 $34.96   13.567%   $39.703   $39.70   $39.70   $39.70  
  Purchase #6 $184.93   5.171%   $194.4927   $194.49   $194.50   $194.50  
  Purchase #7 $121.26   4.285%   $126.456   $126.46   $126.45   $126.50  
  7 purchase totals = $926.49       $992.5766   $992.56   $992.55   $992.60