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 $54.95   4.155%   $57.2332   $57.23   $57.25   $57.20  
  Purchase #2 $233.56   10.587%   $258.287   $258.29   $258.30   $258.30  
  Purchase #3 $23.95   9.268%   $26.1697   $26.17   $26.15   $26.20  
  Purchase #4 $50.32   4.258%   $52.4626   $52.46   $52.45   $52.50  
  Purchase #5 $80.30   11.761%   $89.7441   $89.74   $89.75   $89.70  
  Purchase #6 $212.52   6.430%   $226.185   $226.19   $226.20   $226.20  
  Purchase #7 $202.72   6.869%   $216.6448   $216.64   $216.65   $216.60  
  7 purchase totals = $858.32       $926.7264   $926.72   $926.75   $926.70