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 $48.40   7.874%   $52.211   $52.21   $52.20   $52.20  
  Purchase #2 $88.94   7.412%   $95.5322   $95.53   $95.55   $95.50  
  Purchase #3 $241.94   10.713%   $267.859   $267.86   $267.85   $267.90  
  Purchase #4 $125.73   12.279%   $141.1684   $141.17   $141.15   $141.20  
  Purchase #5 $216.52   10.622%   $239.5188   $239.52   $239.50   $239.50  
  Purchase #6 $204.97   12.662%   $230.9233   $230.92   $230.90   $230.90  
  Purchase #7 $220.82   11.467%   $246.1414   $246.14   $246.15   $246.10  
  7 purchase totals = $1,147.32       $1,273.3541   $1,273.35   $1,273.30   $1,273.30