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 $55.26   11.262%   $61.4834   $61.48   $61.50   $61.50  
  Purchase #2 $98.53   7.802%   $106.2173   $106.22   $106.20   $106.20  
  Purchase #3 $112.55   12.576%   $126.7043   $126.70   $126.70   $126.70  
  Purchase #4 $220.60   6.858%   $235.7287   $235.73   $235.75   $235.70  
  Purchase #5 $87.41   4.740%   $91.5532   $91.55   $91.55   $91.60  
  Purchase #6 $134.85   10.576%   $149.1117   $149.11   $149.10   $149.10  
  Purchase #7 $32.56   10.732%   $36.0543   $36.05   $36.05   $36.10  
  7 purchase totals = $741.76       $806.8529   $806.84   $806.85   $806.90