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 $169.61   8.673%   $184.3203   $184.32   $184.30   $184.30  
  Purchase #2 $92.25   5.647%   $97.4594   $97.46   $97.45   $97.50  
  Purchase #3 $44.95   9.118%   $49.0485   $49.05   $49.05   $49.00  
  Purchase #4 $174.93   10.871%   $193.9466   $193.95   $193.95   $193.90  
  Purchase #5 $47.93   10.144%   $52.792   $52.79   $52.80   $52.80  
  Purchase #6 $55.65   8.393%   $60.3207   $60.32   $60.30   $60.30  
  Purchase #7 $200.83   4.700%   $210.269   $210.27   $210.25   $210.30  
  7 purchase totals = $786.15       $848.1565   $848.16   $848.10   $848.10