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 $47.65   11.140%   $52.9582   $52.96   $52.95   $53.00  
  Purchase #2 $37.50   5.529%   $39.5734   $39.57   $39.55   $39.60  
  Purchase #3 $123.55   10.448%   $136.4585   $136.46   $136.45   $136.50  
  Purchase #4 $244.52   8.262%   $264.7222   $264.72   $264.70   $264.70  
  Purchase #5 $195.44   11.556%   $218.025   $218.03   $218.05   $218.00  
  Purchase #6 $47.83   12.578%   $53.8461   $53.85   $53.85   $53.80  
  Purchase #7 $173.74   7.143%   $186.1502   $186.15   $186.15   $186.20  
  7 purchase totals = $870.23       $951.7336   $951.74   $951.70   $951.80