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 $190.75   7.571%   $205.1917   $205.19   $205.20   $205.20  
  Purchase #2 $206.86   12.148%   $231.9894   $231.99   $232.00   $232.00  
  Purchase #3 $194.91   12.405%   $219.0886   $219.09   $219.10   $219.10  
  Purchase #4 $212.44   9.525%   $232.6749   $232.67   $232.65   $232.70  
  Purchase #5 $119.61   8.312%   $129.552   $129.55   $129.55   $129.60  
  Purchase #6 $110.60   9.797%   $121.4355   $121.44   $121.45   $121.40  
  Purchase #7 $166.72   8.799%   $181.3897   $181.39   $181.40   $181.40  
  7 purchase totals = $1,201.89       $1,321.3218   $1,321.32   $1,321.35   $1,321.40