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 $76.45   3.585%   $79.1907   $79.19   $79.20   $79.20  
  Purchase #2 $224.67   13.481%   $254.9578   $254.96   $254.95   $255.00  
  Purchase #3 $179.82   12.237%   $201.8246   $201.82   $201.80   $201.80  
  Purchase #4 $22.29   9.216%   $24.3442   $24.34   $24.35   $24.30  
  Purchase #5 $78.28   12.380%   $87.9711   $87.97   $87.95   $88.00  
  Purchase #6 $214.41   8.445%   $232.5169   $232.52   $232.50   $232.50  
  Purchase #7 $139.94   11.103%   $155.4775   $155.48   $155.50   $155.50  
  7 purchase totals = $935.86       $1,036.2828   $1,036.28   $1,036.25   $1,036.30