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 $33.51   3.450%   $34.6661   $34.67   $34.65   $34.70  
  Purchase #2 $219.85   5.835%   $232.6782   $232.68   $232.70   $232.70  
  Purchase #3 $225.40   8.618%   $244.825   $244.83   $244.85   $244.80  
  Purchase #4 $242.79   11.736%   $271.2838   $271.28   $271.30   $271.30  
  Purchase #5 $111.85   5.764%   $118.297   $118.30   $118.30   $118.30  
  Purchase #6 $243.40   5.778%   $257.4637   $257.46   $257.45   $257.50  
  Purchase #7 $26.29   10.267%   $28.9892   $28.99   $29.00   $29.00  
  7 purchase totals = $1,103.09       $1,188.2030   $1,188.21   $1,188.25   $1,188.30