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 $181.76   12.767%   $204.9653   $204.97   $204.95   $205.00  
  Purchase #2 $37.26   3.137%   $38.4288   $38.43   $38.45   $38.40  
  Purchase #3 $128.59   4.645%   $134.563   $134.56   $134.55   $134.60  
  Purchase #4 $59.57   4.707%   $62.374   $62.37   $62.35   $62.40  
  Purchase #5 $211.39   6.479%   $225.086   $225.09   $225.10   $225.10  
  Purchase #6 $53.72   12.145%   $60.2443   $60.24   $60.25   $60.20  
  Purchase #7 $185.29   9.240%   $202.4108   $202.41   $202.40   $202.40  
  7 purchase totals = $857.58       $928.0722   $928.07   $928.05   $928.10