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 $201.88   11.442%   $224.9791   $224.98   $225.00   $225.00  
  Purchase #2 $226.42   13.660%   $257.349   $257.35   $257.35   $257.30  
  Purchase #3 $13.27   9.847%   $14.5767   $14.58   $14.60   $14.60  
  Purchase #4 $184.35   10.271%   $203.2846   $203.28   $203.30   $203.30  
  Purchase #5 $204.29   13.621%   $232.1163   $232.12   $232.10   $232.10  
  Purchase #6 $156.82   5.534%   $165.4984   $165.50   $165.50   $165.50  
  Purchase #7 $66.65   13.859%   $75.887   $75.89   $75.90   $75.90  
  7 purchase totals = $1,053.68       $1,173.6911   $1,173.70   $1,173.75   $1,173.70