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 $191.30   6.709%   $204.1343   $204.13   $204.15   $204.10  
  Purchase #2 $127.83   12.515%   $143.8279   $143.83   $143.85   $143.80  
  Purchase #3 $17.41   3.641%   $18.0439   $18.04   $18.05   $18.00  
  Purchase #4 $111.65   11.644%   $124.6505   $124.65   $124.65   $124.70  
  Purchase #5 $148.58   8.568%   $161.3103   $161.31   $161.30   $161.30  
  Purchase #6 $110.46   8.699%   $120.0689   $120.07   $120.05   $120.10  
  Purchase #7 $121.71   9.433%   $133.1909   $133.19   $133.20   $133.20  
  7 purchase totals = $828.94       $905.2267   $905.22   $905.25   $905.20