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 $111.77   12.846%   $126.128   $126.13   $126.15   $126.10  
  Purchase #2 $138.62   10.194%   $152.7509   $152.75   $152.75   $152.80  
  Purchase #3 $23.29   10.838%   $25.8142   $25.81   $25.80   $25.80  
  Purchase #4 $218.39   12.653%   $246.0229   $246.02   $246.00   $246.00  
  Purchase #5 $49.97   10.332%   $55.1329   $55.13   $55.15   $55.10  
  Purchase #6 $215.86   9.586%   $236.5523   $236.55   $236.55   $236.60  
  Purchase #7 $77.78   7.574%   $83.6711   $83.67   $83.65   $83.70  
  7 purchase totals = $835.68       $926.0723   $926.06   $926.05   $926.10