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 $220.94   10.802%   $244.8059   $244.81   $244.80   $244.80  
  Purchase #2 $101.68   11.588%   $113.4627   $113.46   $113.45   $113.50  
  Purchase #3 $21.49   12.152%   $24.1015   $24.10   $24.10   $24.10  
  Purchase #4 $166.40   3.554%   $172.3139   $172.31   $172.30   $172.30  
  Purchase #5 $247.68   7.667%   $266.6696   $266.67   $266.65   $266.70  
  Purchase #6 $201.49   9.867%   $221.371   $221.37   $221.35   $221.40  
  Purchase #7 $19.52   6.779%   $20.8433   $20.84   $20.85   $20.80  
  7 purchase totals = $979.20       $1,063.5679   $1,063.56   $1,063.50   $1,063.60