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 $249.65   13.595%   $283.5899   $283.59   $283.60   $283.60  
  Purchase #2 $29.52   12.108%   $33.0943   $33.09   $33.10   $33.10  
  Purchase #3 $6.96   13.868%   $7.9252   $7.93   $7.95   $7.90  
  Purchase #4 $60.31   5.865%   $63.8472   $63.85   $63.85   $63.80  
  Purchase #5 $188.72   9.512%   $206.671   $206.67   $206.65   $206.70  
  Purchase #6 $249.37   6.529%   $265.6514   $265.65   $265.65   $265.70  
  Purchase #7 $31.48   11.334%   $35.0479   $35.05   $35.05   $35.00  
  7 purchase totals = $816.01       $895.8269   $895.83   $895.85   $895.80