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 $69.86   9.181%   $76.2738   $76.27   $76.25   $76.30  
  Purchase #2 $160.47   8.516%   $174.1356   $174.14   $174.15   $174.10  
  Purchase #3 $202.41   8.821%   $220.2646   $220.26   $220.25   $220.30  
  Purchase #4 $74.60   3.554%   $77.2513   $77.25   $77.25   $77.30  
  Purchase #5 $69.53   11.532%   $77.5482   $77.55   $77.55   $77.50  
  Purchase #6 $205.37   11.243%   $228.4597   $228.46   $228.45   $228.50  
  Purchase #7 $149.65   11.196%   $166.4048   $166.40   $166.40   $166.40  
  7 purchase totals = $931.89       $1,020.3380   $1,020.33   $1,020.30   $1,020.40