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 $65.25   9.362%   $71.3587   $71.36   $71.35   $71.40  
  Purchase #2 $54.31   13.872%   $61.8439   $61.84   $61.85   $61.80  
  Purchase #3 $158.49   6.327%   $168.5177   $168.52   $168.50   $168.50  
  Purchase #4 $246.36   13.479%   $279.5669   $279.57   $279.55   $279.60  
  Purchase #5 $62.33   7.391%   $66.9368   $66.94   $66.95   $66.90  
  Purchase #6 $232.50   9.246%   $253.997   $254.00   $254.00   $254.00  
  Purchase #7 $92.63   6.180%   $98.3545   $98.35   $98.35   $98.40  
  7 purchase totals = $911.87       $1,000.5755   $1,000.58   $1,000.55   $1,000.60