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 $91.69   5.232%   $96.4872   $96.49   $96.50   $96.50  
  Purchase #2 $95.28   3.512%   $98.6262   $98.63   $98.65   $98.60  
  Purchase #3 $202.42   11.447%   $225.591   $225.59   $225.60   $225.60  
  Purchase #4 $7.86   12.699%   $8.8581   $8.86   $8.85   $8.90  
  Purchase #5 $187.46   8.732%   $203.829   $203.83   $203.85   $203.80  
  Purchase #6 $83.36   13.448%   $94.5703   $94.57   $94.55   $94.60  
  Purchase #7 $203.29   4.538%   $212.5153   $212.52   $212.50   $212.50  
  7 purchase totals = $871.36       $940.4771   $940.49   $940.50   $940.50