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 $148.75   6.318%   $158.148   $158.15   $158.15   $158.10  
  Purchase #2 $115.28   6.411%   $122.6706   $122.67   $122.65   $122.70  
  Purchase #3 $39.81   3.270%   $41.1118   $41.11   $41.10   $41.10  
  Purchase #4 $190.97   6.306%   $203.0126   $203.01   $203.00   $203.00  
  Purchase #5 $99.80   5.546%   $105.3349   $105.33   $105.35   $105.30  
  Purchase #6 $191.86   8.426%   $208.0261   $208.03   $208.05   $208.00  
  Purchase #7 $6.42   5.352%   $6.7636   $6.76   $6.75   $6.80  
  7 purchase totals = $792.89       $845.0676   $845.06   $845.05   $845.00