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 $198.44   4.141%   $206.6574   $206.66   $206.65   $206.70  
  Purchase #2 $29.86   9.197%   $32.6062   $32.61   $32.60   $32.60  
  Purchase #3 $164.75   9.662%   $180.6681   $180.67   $180.65   $180.70  
  Purchase #4 $30.33   5.357%   $31.9548   $31.95   $31.95   $32.00  
  Purchase #5 $145.79   9.191%   $159.1896   $159.19   $159.20   $159.20  
  Purchase #6 $144.31   5.692%   $152.5241   $152.52   $152.50   $152.50  
  Purchase #7 $217.67   11.290%   $242.2449   $242.24   $242.25   $242.20  
  7 purchase totals = $931.15       $1,005.8451   $1,005.84   $1,005.80   $1,005.90