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 $118.42   6.572%   $126.2026   $126.20   $126.20   $126.20  
  Purchase #2 $48.82   10.143%   $53.7718   $53.77   $53.75   $53.80  
  Purchase #3 $238.61   12.529%   $268.5054   $268.51   $268.50   $268.50  
  Purchase #4 $39.53   13.187%   $44.7428   $44.74   $44.75   $44.70  
  Purchase #5 $135.61   8.561%   $147.2196   $147.22   $147.20   $147.20  
  Purchase #6 $85.31   9.715%   $93.5979   $93.60   $93.60   $93.60  
  Purchase #7 $116.94   11.700%   $130.622   $130.62   $130.60   $130.60  
  7 purchase totals = $783.24       $864.6621   $864.66   $864.60   $864.60