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 $162.44   4.766%   $170.1819   $170.18   $170.20   $170.20  
  Purchase #2 $123.41   12.190%   $138.4537   $138.45   $138.45   $138.50  
  Purchase #3 $148.48   3.198%   $153.2284   $153.23   $153.25   $153.20  
  Purchase #4 $158.58   4.717%   $166.0602   $166.06   $166.05   $166.10  
  Purchase #5 $218.30   6.421%   $232.317   $232.32   $232.30   $232.30  
  Purchase #6 $237.81   9.679%   $260.8276   $260.83   $260.85   $260.80  
  Purchase #7 $118.25   11.419%   $131.753   $131.75   $131.75   $131.80  
  7 purchase totals = $1,167.27       $1,252.8218   $1,252.82   $1,252.85   $1,252.90