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 $54.90   10.179%   $60.4883   $60.49   $60.50   $60.50  
  Purchase #2 $69.52   3.492%   $71.9476   $71.95   $71.95   $71.90  
  Purchase #3 $90.84   4.872%   $95.2657   $95.27   $95.25   $95.30  
  Purchase #4 $160.40   9.207%   $175.168   $175.17   $175.15   $175.20  
  Purchase #5 $138.53   9.570%   $151.7873   $151.79   $151.80   $151.80  
  Purchase #6 $208.94   13.222%   $236.566   $236.57   $236.55   $236.60  
  Purchase #7 $219.49   12.573%   $247.0865   $247.09   $247.10   $247.10  
  7 purchase totals = $942.62       $1,038.3094   $1,038.33   $1,038.30   $1,038.40