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 $58.28   4.802%   $61.0786   $61.08   $61.10   $61.10  
  Purchase #2 $167.90   6.521%   $178.8488   $178.85   $178.85   $178.80  
  Purchase #3 $206.49   8.431%   $223.8992   $223.90   $223.90   $223.90  
  Purchase #4 $207.35   6.840%   $221.5327   $221.53   $221.55   $221.50  
  Purchase #5 $166.61   13.575%   $189.2273   $189.23   $189.25   $189.20  
  Purchase #6 $117.98   8.463%   $127.9646   $127.96   $127.95   $128.00  
  Purchase #7 $63.57   13.421%   $72.1017   $72.10   $72.10   $72.10  
  7 purchase totals = $988.18       $1,074.6529   $1,074.65   $1,074.70   $1,074.60