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 $187.70   8.206%   $203.1027   $203.10   $203.10   $203.10  
  Purchase #2 $120.66   8.405%   $130.8015   $130.80   $130.80   $130.80  
  Purchase #3 $241.48   10.159%   $266.012   $266.01   $266.00   $266.00  
  Purchase #4 $47.83   6.584%   $50.9791   $50.98   $51.00   $51.00  
  Purchase #5 $107.92   5.257%   $113.5934   $113.59   $113.60   $113.60  
  Purchase #6 $171.85   4.227%   $179.1141   $179.11   $179.10   $179.10  
  Purchase #7 $62.65   9.846%   $68.8185   $68.82   $68.80   $68.80  
  7 purchase totals = $940.09       $1,012.4213   $1,012.41   $1,012.40   $1,012.40