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 $26.74   6.787%   $28.5548   $28.55   $28.55   $28.60  
  Purchase #2 $234.27   12.674%   $263.9614   $263.96   $263.95   $264.00  
  Purchase #3 $49.49   11.124%   $54.9953   $55.00   $55.00   $55.00  
  Purchase #4 $212.58   9.604%   $232.9962   $233.00   $233.00   $233.00  
  Purchase #5 $48.52   8.328%   $52.5607   $52.56   $52.55   $52.60  
  Purchase #6 $106.44   6.367%   $113.217   $113.22   $113.20   $113.20  
  Purchase #7 $243.55   12.773%   $274.6586   $274.66   $274.65   $274.70  
  7 purchase totals = $921.59       $1,020.9440   $1,020.95   $1,020.90   $1,021.10