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 $212.65   6.590%   $226.6636   $226.66   $226.65   $226.70  
  Purchase #2 $127.80   8.337%   $138.4547   $138.45   $138.45   $138.50  
  Purchase #3 $135.31   6.611%   $144.2553   $144.26   $144.25   $144.30  
  Purchase #4 $116.72   7.173%   $125.0923   $125.09   $125.10   $125.10  
  Purchase #5 $184.70   13.719%   $210.039   $210.04   $210.05   $210.00  
  Purchase #6 $162.98   5.349%   $171.6978   $171.70   $171.70   $171.70  
  Purchase #7 $219.97   9.240%   $240.2952   $240.30   $240.30   $240.30  
  7 purchase totals = $1,160.13       $1,256.4979   $1,256.50   $1,256.50   $1,256.60