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 $184.94   9.760%   $202.9901   $202.99   $203.00   $203.00  
  Purchase #2 $8.66   10.392%   $9.5599   $9.56   $9.55   $9.60  
  Purchase #3 $244.26   8.484%   $264.983   $264.98   $265.00   $265.00  
  Purchase #4 $131.74   8.253%   $142.6125   $142.61   $142.60   $142.60  
  Purchase #5 $196.27   11.808%   $219.4456   $219.45   $219.45   $219.40  
  Purchase #6 $89.88   6.396%   $95.6287   $95.63   $95.65   $95.60  
  Purchase #7 $62.91   7.489%   $67.6213   $67.62   $67.60   $67.60  
  7 purchase totals = $918.66       $1,002.8411   $1,002.84   $1,002.85   $1,002.80