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 $153.65   13.327%   $174.1269   $174.13   $174.15   $174.10  
  Purchase #2 $206.88   7.292%   $221.9657   $221.97   $221.95   $222.00  
  Purchase #3 $222.97   3.805%   $231.454   $231.45   $231.45   $231.50  
  Purchase #4 $72.50   4.128%   $75.4928   $75.49   $75.50   $75.50  
  Purchase #5 $209.76   4.395%   $218.979   $218.98   $219.00   $219.00  
  Purchase #6 $247.74   8.206%   $268.0695   $268.07   $268.05   $268.10  
  Purchase #7 $160.66   8.124%   $173.712   $173.71   $173.70   $173.70  
  7 purchase totals = $1,274.16       $1,363.7999   $1,363.80   $1,363.80   $1,363.90