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 $71.30   3.613%   $73.8761   $73.88   $73.90   $73.90  
  Purchase #2 $139.75   7.794%   $150.6421   $150.64   $150.65   $150.60  
  Purchase #3 $128.93   4.777%   $135.089   $135.09   $135.10   $135.10  
  Purchase #4 $215.32   4.381%   $224.7532   $224.75   $224.75   $224.80  
  Purchase #5 $215.87   9.279%   $235.9006   $235.90   $235.90   $235.90  
  Purchase #6 $88.51   4.820%   $92.7762   $92.78   $92.80   $92.80  
  Purchase #7 $184.29   9.660%   $202.0924   $202.09   $202.10   $202.10  
  7 purchase totals = $1,043.97       $1,115.1296   $1,115.13   $1,115.20   $1,115.20