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 $38.32   13.813%   $43.6131   $43.61   $43.60   $43.60  
  Purchase #2 $192.68   9.510%   $211.0039   $211.00   $211.00   $211.00  
  Purchase #3 $173.80   7.581%   $186.9758   $186.98   $187.00   $187.00  
  Purchase #4 $159.46   13.251%   $180.59   $180.59   $180.60   $180.60  
  Purchase #5 $8.60   11.761%   $9.6114   $9.61   $9.60   $9.60  
  Purchase #6 $242.83   6.123%   $257.6985   $257.70   $257.70   $257.70  
  Purchase #7 $102.79   10.614%   $113.7001   $113.70   $113.70   $113.70  
  7 purchase totals = $918.48       $1,003.1928   $1,003.19   $1,003.20   $1,003.20