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 $141.81   7.311%   $152.1777   $152.18   $152.20   $152.20  
  Purchase #2 $77.37   6.810%   $82.6389   $82.64   $82.65   $82.60  
  Purchase #3 $125.33   7.718%   $135.003   $135.00   $135.00   $135.00  
  Purchase #4 $84.84   10.329%   $93.6031   $93.60   $93.60   $93.60  
  Purchase #5 $192.94   12.200%   $216.4787   $216.48   $216.50   $216.50  
  Purchase #6 $53.41   9.405%   $58.4332   $58.43   $58.45   $58.40  
  Purchase #7 $25.91   4.623%   $27.1078   $27.11   $27.10   $27.10  
  7 purchase totals = $701.61       $765.4424   $765.44   $765.50   $765.40