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 $150.44   8.364%   $163.0228   $163.02   $163.00   $163.00  
  Purchase #2 $22.51   7.145%   $24.1183   $24.12   $24.10   $24.10  
  Purchase #3 $43.78   8.874%   $47.665   $47.67   $47.65   $47.70  
  Purchase #4 $122.79   9.351%   $134.2721   $134.27   $134.25   $134.30  
  Purchase #5 $244.57   12.762%   $275.782   $275.78   $275.80   $275.80  
  Purchase #6 $249.74   8.392%   $270.6982   $270.70   $270.70   $270.70  
  Purchase #7 $116.50   11.355%   $129.7286   $129.73   $129.75   $129.70  
  7 purchase totals = $950.33       $1,045.2870   $1,045.29   $1,045.25   $1,045.30