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 $144.73   11.787%   $161.7893   $161.79   $161.80   $161.80  
  Purchase #2 $180.65   8.409%   $195.8409   $195.84   $195.85   $195.80  
  Purchase #3 $46.27   8.217%   $50.072   $50.07   $50.05   $50.10  
  Purchase #4 $176.43   9.287%   $192.8151   $192.82   $192.80   $192.80  
  Purchase #5 $137.83   5.117%   $144.8828   $144.88   $144.90   $144.90  
  Purchase #6 $115.38   5.270%   $121.4605   $121.46   $121.45   $121.50  
  Purchase #7 $191.59   4.137%   $199.5161   $199.52   $199.50   $199.50  
  7 purchase totals = $992.88       $1,066.3767   $1,066.38   $1,066.35   $1,066.40