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 $71.78   3.354%   $74.1875   $74.19   $74.20   $74.20  
  Purchase #2 $217.84   4.453%   $227.5404   $227.54   $227.55   $227.50  
  Purchase #3 $62.59   11.759%   $69.95   $69.95   $69.95   $70.00  
  Purchase #4 $174.92   8.692%   $190.124   $190.12   $190.10   $190.10  
  Purchase #5 $134.53   9.298%   $147.0386   $147.04   $147.05   $147.00  
  Purchase #6 $59.71   4.183%   $62.2077   $62.21   $62.20   $62.20  
  Purchase #7 $232.80   3.425%   $240.7734   $240.77   $240.75   $240.80  
  7 purchase totals = $954.17       $1,011.8216   $1,011.82   $1,011.80   $1,011.80