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 $181.41   11.556%   $202.3737   $202.37   $202.35   $202.40  
  Purchase #2 $68.38   4.166%   $71.2287   $71.23   $71.25   $71.20  
  Purchase #3 $190.72   11.780%   $213.1868   $213.19   $213.20   $213.20  
  Purchase #4 $89.30   6.748%   $95.326   $95.33   $95.35   $95.30  
  Purchase #5 $224.26   11.279%   $249.5543   $249.55   $249.55   $249.60  
  Purchase #6 $232.57   4.700%   $243.5008   $243.50   $243.50   $243.50  
  Purchase #7 $210.61   4.191%   $219.4367   $219.44   $219.45   $219.40  
  7 purchase totals = $1,197.25       $1,294.6070   $1,294.61   $1,294.65   $1,294.60