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 $58.97   8.184%   $63.7961   $63.80   $63.80   $63.80  
  Purchase #2 $19.47   6.725%   $20.7794   $20.78   $20.80   $20.80  
  Purchase #3 $166.38   4.621%   $174.0684   $174.07   $174.05   $174.10  
  Purchase #4 $110.77   8.765%   $120.479   $120.48   $120.50   $120.50  
  Purchase #5 $56.99   9.686%   $62.5101   $62.51   $62.50   $62.50  
  Purchase #6 $90.30   8.753%   $98.204   $98.20   $98.20   $98.20  
  Purchase #7 $150.29   3.483%   $155.5246   $155.52   $155.50   $155.50  
  7 purchase totals = $653.17       $695.3616   $695.36   $695.35   $695.40