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 $63.59   12.707%   $71.6704   $71.67   $71.65   $71.70  
  Purchase #2 $230.96   9.264%   $252.3561   $252.36   $252.35   $252.40  
  Purchase #3 $56.80   8.753%   $61.7717   $61.77   $61.75   $61.80  
  Purchase #4 $92.91   3.508%   $96.1693   $96.17   $96.15   $96.20  
  Purchase #5 $81.74   12.773%   $92.1807   $92.18   $92.20   $92.20  
  Purchase #6 $60.49   6.785%   $64.5942   $64.59   $64.60   $64.60  
  Purchase #7 $100.89   7.161%   $108.1147   $108.11   $108.10   $108.10  
  7 purchase totals = $687.38       $746.8571   $746.85   $746.80   $747.00