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 $88.59   6.418%   $94.2757   $94.28   $94.30   $94.30  
  Purchase #2 $136.43   11.645%   $152.3173   $152.32   $152.30   $152.30  
  Purchase #3 $194.71   13.223%   $220.4565   $220.46   $220.45   $220.50  
  Purchase #4 $229.84   13.542%   $260.9649   $260.96   $260.95   $261.00  
  Purchase #5 $59.61   11.173%   $66.2702   $66.27   $66.25   $66.30  
  Purchase #6 $210.67   13.772%   $239.6835   $239.68   $239.70   $239.70  
  Purchase #7 $128.88   12.727%   $145.2826   $145.28   $145.30   $145.30  
  7 purchase totals = $1,048.73       $1,179.2507   $1,179.25   $1,179.25   $1,179.40