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 $33.68   12.200%   $37.789   $37.79   $37.80   $37.80  
  Purchase #2 $55.89   10.845%   $61.9513   $61.95   $61.95   $62.00  
  Purchase #3 $133.97   10.413%   $147.9203   $147.92   $147.90   $147.90  
  Purchase #4 $244.87   12.535%   $275.5645   $275.56   $275.55   $275.60  
  Purchase #5 $219.98   7.663%   $236.8371   $236.84   $236.85   $236.80  
  Purchase #6 $176.73   6.516%   $188.2457   $188.25   $188.25   $188.20  
  Purchase #7 $216.27   5.705%   $228.6082   $228.61   $228.60   $228.60  
  7 purchase totals = $1,081.39       $1,176.9161   $1,176.92   $1,176.90   $1,176.90