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 $54.37   11.137%   $60.4252   $60.43   $60.45   $60.40  
  Purchase #2 $233.75   13.759%   $265.9117   $265.91   $265.90   $265.90  
  Purchase #3 $217.77   5.389%   $229.5056   $229.51   $229.50   $229.50  
  Purchase #4 $71.25   6.376%   $75.7929   $75.79   $75.80   $75.80  
  Purchase #5 $223.86   10.344%   $247.0161   $247.02   $247.00   $247.00  
  Purchase #6 $53.92   5.337%   $56.7977   $56.80   $56.80   $56.80  
  Purchase #7 $168.50   7.858%   $181.7407   $181.74   $181.75   $181.70  
  7 purchase totals = $1,023.42       $1,117.1899   $1,117.20   $1,117.20   $1,117.10