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 $182.29   5.272%   $191.9003   $191.90   $191.90   $191.90  
  Purchase #2 $136.32   4.575%   $142.5566   $142.56   $142.55   $142.60  
  Purchase #3 $132.32   10.414%   $146.0998   $146.10   $146.10   $146.10  
  Purchase #4 $66.96   11.339%   $74.5526   $74.55   $74.55   $74.60  
  Purchase #5 $41.95   6.568%   $44.7053   $44.71   $44.70   $44.70  
  Purchase #6 $232.28   5.483%   $245.0159   $245.02   $245.00   $245.00  
  Purchase #7 $115.55   5.289%   $121.6614   $121.66   $121.65   $121.70  
  7 purchase totals = $907.67       $966.4919   $966.50   $966.45   $966.60