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 $120.55   11.154%   $133.9961   $134.00   $134.00   $134.00  
  Purchase #2 $59.53   3.161%   $61.4117   $61.41   $61.40   $61.40  
  Purchase #3 $227.64   13.172%   $257.6247   $257.62   $257.60   $257.60  
  Purchase #4 $152.48   5.364%   $160.659   $160.66   $160.65   $160.70  
  Purchase #5 $89.67   3.163%   $92.5063   $92.51   $92.50   $92.50  
  Purchase #6 $137.68   8.255%   $149.0455   $149.05   $149.05   $149.00  
  Purchase #7 $162.78   3.169%   $167.9385   $167.94   $167.95   $167.90  
  7 purchase totals = $950.33       $1,023.1818   $1,023.19   $1,023.15   $1,023.10