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 $116.44   10.477%   $128.6394   $128.64   $128.65   $128.60  
  Purchase #2 $133.36   13.779%   $151.7357   $151.74   $151.75   $151.70  
  Purchase #3 $167.80   5.311%   $176.7119   $176.71   $176.70   $176.70  
  Purchase #4 $198.41   4.150%   $206.644   $206.64   $206.65   $206.60  
  Purchase #5 $56.50   13.323%   $64.0275   $64.03   $64.05   $64.00  
  Purchase #6 $167.37   8.657%   $181.8592   $181.86   $181.85   $181.90  
  Purchase #7 $103.82   6.454%   $110.5205   $110.52   $110.50   $110.50  
  7 purchase totals = $943.70       $1,020.1382   $1,020.14   $1,020.15   $1,020.00