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 $245.66   11.293%   $273.4024   $273.40   $273.40   $273.40  
  Purchase #2 $135.83   10.862%   $150.5839   $150.58   $150.60   $150.60  
  Purchase #3 $23.62   6.391%   $25.1296   $25.13   $25.15   $25.10  
  Purchase #4 $228.41   6.640%   $243.5764   $243.58   $243.60   $243.60  
  Purchase #5 $205.64   8.843%   $223.8247   $223.82   $223.80   $223.80  
  Purchase #6 $155.74   11.517%   $173.6766   $173.68   $173.70   $173.70  
  Purchase #7 $22.57   12.663%   $25.428   $25.43   $25.45   $25.40  
  7 purchase totals = $1,017.47       $1,115.6216   $1,115.62   $1,115.70   $1,115.60