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 $212.29   5.735%   $224.4648   $224.46   $224.45   $224.50  
  Purchase #2 $147.48   11.819%   $164.9107   $164.91   $164.90   $164.90  
  Purchase #3 $130.38   4.717%   $136.53   $136.53   $136.55   $136.50  
  Purchase #4 $192.50   5.117%   $202.3502   $202.35   $202.35   $202.40  
  Purchase #5 $30.84   6.306%   $32.7848   $32.78   $32.80   $32.80  
  Purchase #6 $225.46   9.581%   $247.0613   $247.06   $247.05   $247.10  
  Purchase #7 $23.81   6.840%   $25.4386   $25.44   $25.45   $25.40  
  7 purchase totals = $962.76       $1,033.5404   $1,033.53   $1,033.55   $1,033.60