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 $150.59   7.121%   $161.3135   $161.31   $161.30   $161.30  
  Purchase #2 $232.78   3.616%   $241.1973   $241.20   $241.20   $241.20  
  Purchase #3 $161.77   13.739%   $183.9956   $184.00   $184.00   $184.00  
  Purchase #4 $228.66   5.225%   $240.6075   $240.61   $240.60   $240.60  
  Purchase #5 $168.55   12.388%   $189.43   $189.43   $189.45   $189.40  
  Purchase #6 $146.50   11.809%   $163.8002   $163.80   $163.80   $163.80  
  Purchase #7 $217.86   13.243%   $246.7112   $246.71   $246.70   $246.70  
  7 purchase totals = $1,306.71       $1,427.0553   $1,427.06   $1,427.05   $1,427.00