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 $83.69   10.233%   $92.254   $92.25   $92.25   $92.30  
  Purchase #2 $159.94   5.295%   $168.4088   $168.41   $168.40   $168.40  
  Purchase #3 $6.88   11.238%   $7.6532   $7.65   $7.65   $7.70  
  Purchase #4 $62.78   11.797%   $70.1862   $70.19   $70.20   $70.20  
  Purchase #5 $47.45   13.463%   $53.8382   $53.84   $53.85   $53.80  
  Purchase #6 $147.89   9.219%   $161.524   $161.52   $161.50   $161.50  
  Purchase #7 $230.98   8.469%   $250.5417   $250.54   $250.55   $250.50  
  7 purchase totals = $739.61       $804.4061   $804.40   $804.40   $804.40