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 $108.84   4.121%   $113.3253   $113.33   $113.35   $113.30  
  Purchase #2 $126.43   7.196%   $135.5279   $135.53   $135.55   $135.50  
  Purchase #3 $5.70   8.203%   $6.1676   $6.17   $6.15   $6.20  
  Purchase #4 $59.26   10.221%   $65.317   $65.32   $65.30   $65.30  
  Purchase #5 $10.64   13.764%   $12.1045   $12.10   $12.10   $12.10  
  Purchase #6 $169.87   9.669%   $186.2947   $186.29   $186.30   $186.30  
  Purchase #7 $48.82   8.695%   $53.0649   $53.06   $53.05   $53.10  
  7 purchase totals = $529.56       $571.8019   $571.80   $571.80   $571.80