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 $45.53   10.519%   $50.3193   $50.32   $50.30   $50.30  
  Purchase #2 $65.87   4.523%   $68.8493   $68.85   $68.85   $68.80  
  Purchase #3 $118.53   8.163%   $128.2056   $128.21   $128.20   $128.20  
  Purchase #4 $218.83   12.655%   $246.5229   $246.52   $246.50   $246.50  
  Purchase #5 $228.95   12.235%   $256.962   $256.96   $256.95   $257.00  
  Purchase #6 $236.71   4.778%   $248.02   $248.02   $248.00   $248.00  
  Purchase #7 $10.62   12.591%   $11.9572   $11.96   $11.95   $12.00  
  7 purchase totals = $925.04       $1,010.8363   $1,010.84   $1,010.75   $1,010.80