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 $53.57   11.681%   $59.8275   $59.83   $59.85   $59.80  
  Purchase #2 $120.94   9.829%   $132.8272   $132.83   $132.85   $132.80  
  Purchase #3 $192.30   9.828%   $211.1992   $211.20   $211.20   $211.20  
  Purchase #4 $97.72   10.514%   $107.9943   $107.99   $108.00   $108.00  
  Purchase #5 $172.45   3.592%   $178.6444   $178.64   $178.65   $178.60  
  Purchase #6 $110.55   10.367%   $122.0107   $122.01   $122.00   $122.00  
  Purchase #7 $75.80   10.665%   $83.8841   $83.88   $83.90   $83.90  
  7 purchase totals = $823.33       $896.3874   $896.38   $896.45   $896.30