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 $228.43   13.719%   $259.7683   $259.77   $259.75   $259.80  
  Purchase #2 $230.49   5.426%   $242.9964   $243.00   $243.00   $243.00  
  Purchase #3 $39.41   12.482%   $44.3292   $44.33   $44.35   $44.30  
  Purchase #4 $162.83   5.350%   $171.5414   $171.54   $171.55   $171.50  
  Purchase #5 $5.99   5.306%   $6.3078   $6.31   $6.30   $6.30  
  Purchase #6 $177.99   9.312%   $194.5644   $194.56   $194.55   $194.60  
  Purchase #7 $216.84   4.456%   $226.5024   $226.50   $226.50   $226.50  
  7 purchase totals = $1,061.98       $1,146.0099   $1,146.01   $1,146.00   $1,146.00