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 $91.56   5.645%   $96.7286   $96.73   $96.75   $96.70  
  Purchase #2 $118.77   11.440%   $132.3573   $132.36   $132.35   $132.40  
  Purchase #3 $58.27   12.772%   $65.7122   $65.71   $65.70   $65.70  
  Purchase #4 $35.25   7.185%   $37.7827   $37.78   $37.80   $37.80  
  Purchase #5 $99.73   4.735%   $104.4522   $104.45   $104.45   $104.50  
  Purchase #6 $186.71   3.514%   $193.271   $193.27   $193.25   $193.30  
  Purchase #7 $219.44   9.837%   $241.0263   $241.03   $241.05   $241.00  
  7 purchase totals = $809.73       $871.3303   $871.33   $871.35   $871.40