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 $176.46   11.645%   $197.0088   $197.01   $197.00   $197.00  
  Purchase #2 $94.80   11.322%   $105.5333   $105.53   $105.55   $105.50  
  Purchase #3 $106.85   11.200%   $118.8172   $118.82   $118.80   $118.80  
  Purchase #4 $25.71   10.686%   $28.4574   $28.46   $28.45   $28.50  
  Purchase #5 $206.84   11.336%   $230.2874   $230.29   $230.30   $230.30  
  Purchase #6 $185.86   13.432%   $210.8247   $210.82   $210.80   $210.80  
  Purchase #7 $150.26   4.272%   $156.6791   $156.68   $156.70   $156.70  
  7 purchase totals = $946.78       $1,047.6079   $1,047.61   $1,047.60   $1,047.60