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 $48.27   12.586%   $54.3453   $54.35   $54.35   $54.30  
  Purchase #2 $191.53   13.145%   $216.7066   $216.71   $216.70   $216.70  
  Purchase #3 $233.39   11.782%   $260.888   $260.89   $260.90   $260.90  
  Purchase #4 $204.31   7.691%   $220.0235   $220.02   $220.00   $220.00  
  Purchase #5 $104.73   12.495%   $117.816   $117.82   $117.80   $117.80  
  Purchase #6 $215.54   11.157%   $239.5878   $239.59   $239.60   $239.60  
  Purchase #7 $127.55   6.386%   $135.6953   $135.70   $135.70   $135.70  
  7 purchase totals = $1,125.32       $1,245.0625   $1,245.08   $1,245.05   $1,245.00