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 $186.81   3.471%   $193.2942   $193.29   $193.30   $193.30  
  Purchase #2 $81.82   11.222%   $91.0018   $91.00   $91.00   $91.00  
  Purchase #3 $71.38   4.716%   $74.7463   $74.75   $74.75   $74.70  
  Purchase #4 $112.32   5.400%   $118.3853   $118.39   $118.40   $118.40  
  Purchase #5 $244.87   12.350%   $275.1114   $275.11   $275.10   $275.10  
  Purchase #6 $123.59   3.740%   $128.2123   $128.21   $128.20   $128.20  
  Purchase #7 $176.42   5.761%   $186.5836   $186.58   $186.60   $186.60  
  7 purchase totals = $997.21       $1,067.3349   $1,067.33   $1,067.35   $1,067.30