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 $33.62   4.662%   $35.1874   $35.19   $35.20   $35.20  
  Purchase #2 $110.72   13.557%   $125.7303   $125.73   $125.75   $125.70  
  Purchase #3 $28.71   8.158%   $31.0522   $31.05   $31.05   $31.10  
  Purchase #4 $145.52   5.364%   $153.3257   $153.33   $153.35   $153.30  
  Purchase #5 $171.55   12.451%   $192.9097   $192.91   $192.90   $192.90  
  Purchase #6 $236.30   10.381%   $260.8303   $260.83   $260.85   $260.80  
  Purchase #7 $156.95   12.779%   $177.0066   $177.01   $177.00   $177.00  
  7 purchase totals = $883.37       $976.0422   $976.05   $976.10   $976.00