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 $197.94   8.144%   $214.0602   $214.06   $214.05   $214.10  
  Purchase #2 $221.42   13.686%   $251.7235   $251.72   $251.70   $251.70  
  Purchase #3 $43.86   12.392%   $49.2951   $49.30   $49.30   $49.30  
  Purchase #4 $129.63   13.132%   $146.653   $146.65   $146.65   $146.70  
  Purchase #5 $227.45   7.594%   $244.7226   $244.72   $244.70   $244.70  
  Purchase #6 $8.91   7.435%   $9.5725   $9.57   $9.55   $9.60  
  Purchase #7 $79.40   7.691%   $85.5067   $85.51   $85.50   $85.50  
  7 purchase totals = $908.61       $1,001.5336   $1,001.53   $1,001.45   $1,001.60