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 $49.58   8.847%   $53.9663   $53.97   $53.95   $54.00  
  Purchase #2 $244.39   3.106%   $251.9808   $251.98   $252.00   $252.00  
  Purchase #3 $75.67   3.715%   $78.4811   $78.48   $78.50   $78.50  
  Purchase #4 $138.50   6.421%   $147.3931   $147.39   $147.40   $147.40  
  Purchase #5 $210.87   5.700%   $222.8896   $222.89   $222.90   $222.90  
  Purchase #6 $39.26   10.240%   $43.2802   $43.28   $43.30   $43.30  
  Purchase #7 $184.53   10.137%   $203.2358   $203.24   $203.25   $203.20  
  7 purchase totals = $942.80       $1,001.2269   $1,001.23   $1,001.30   $1,001.30