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 $35.43   6.351%   $37.6802   $37.68   $37.70   $37.70  
  Purchase #2 $235.64   13.417%   $267.2558   $267.26   $267.25   $267.30  
  Purchase #3 $154.88   11.387%   $172.5162   $172.52   $172.50   $172.50  
  Purchase #4 $37.48   5.278%   $39.4582   $39.46   $39.45   $39.50  
  Purchase #5 $185.27   9.150%   $202.2222   $202.22   $202.20   $202.20  
  Purchase #6 $204.26   9.612%   $223.8935   $223.89   $223.90   $223.90  
  Purchase #7 $152.91   4.141%   $159.242   $159.24   $159.25   $159.20  
  7 purchase totals = $1,005.87       $1,102.2681   $1,102.27   $1,102.25   $1,102.30