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 $88.39   8.554%   $95.9509   $95.95   $95.95   $96.00  
  Purchase #2 $181.85   11.605%   $202.9537   $202.95   $202.95   $203.00  
  Purchase #3 $151.42   4.616%   $158.4095   $158.41   $158.40   $158.40  
  Purchase #4 $83.40   6.495%   $88.8168   $88.82   $88.80   $88.80  
  Purchase #5 $67.93   13.777%   $77.2887   $77.29   $77.30   $77.30  
  Purchase #6 $35.85   9.227%   $39.1579   $39.16   $39.15   $39.20  
  Purchase #7 $29.97   3.639%   $31.0606   $31.06   $31.05   $31.10  
  7 purchase totals = $638.81       $693.6381   $693.64   $693.60   $693.80