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 $182.57   10.686%   $202.0794   $202.08   $202.10   $202.10  
  Purchase #2 $167.57   9.611%   $183.6752   $183.68   $183.70   $183.70  
  Purchase #3 $213.92   11.390%   $238.2855   $238.29   $238.30   $238.30  
  Purchase #4 $32.76   4.695%   $34.2981   $34.30   $34.30   $34.30  
  Purchase #5 $169.38   11.686%   $189.1737   $189.17   $189.15   $189.20  
  Purchase #6 $201.76   7.156%   $216.1979   $216.20   $216.20   $216.20  
  Purchase #7 $204.92   9.807%   $225.0165   $225.02   $225.00   $225.00  
  7 purchase totals = $1,172.88       $1,288.7263   $1,288.74   $1,288.75   $1,288.80