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 $23.64   4.758%   $24.7648   $24.76   $24.75   $24.80  
  Purchase #2 $210.72   10.641%   $233.1427   $233.14   $233.15   $233.10  
  Purchase #3 $203.86   10.851%   $225.9808   $225.98   $226.00   $226.00  
  Purchase #4 $244.76   10.623%   $270.7609   $270.76   $270.75   $270.80  
  Purchase #5 $190.33   7.455%   $204.5191   $204.52   $204.50   $204.50  
  Purchase #6 $244.25   7.339%   $262.1755   $262.18   $262.20   $262.20  
  Purchase #7 $169.82   9.777%   $186.4233   $186.42   $186.40   $186.40  
  7 purchase totals = $1,287.38       $1,407.7671   $1,407.76   $1,407.75   $1,407.80