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 $178.43   13.452%   $202.4324   $202.43   $202.45   $202.40  
  Purchase #2 $122.31   10.555%   $135.2198   $135.22   $135.20   $135.20  
  Purchase #3 $45.68   5.186%   $48.049   $48.05   $48.05   $48.00  
  Purchase #4 $152.64   11.130%   $169.6288   $169.63   $169.65   $169.60  
  Purchase #5 $249.78   11.505%   $278.5172   $278.52   $278.50   $278.50  
  Purchase #6 $159.47   8.267%   $172.6534   $172.65   $172.65   $172.70  
  Purchase #7 $160.55   9.277%   $175.4442   $175.44   $175.45   $175.40  
  7 purchase totals = $1,068.86       $1,181.9448   $1,181.94   $1,181.95   $1,181.80