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 $181.32   11.456%   $202.092   $202.09   $202.10   $202.10  
  Purchase #2 $204.41   9.522%   $223.8739   $223.87   $223.85   $223.90  
  Purchase #3 $127.38   5.455%   $134.3286   $134.33   $134.35   $134.30  
  Purchase #4 $59.85   6.399%   $63.6798   $63.68   $63.70   $63.70  
  Purchase #5 $242.97   12.646%   $273.696   $273.70   $273.70   $273.70  
  Purchase #6 $139.59   11.188%   $155.2073   $155.21   $155.20   $155.20  
  Purchase #7 $23.73   6.606%   $25.2976   $25.30   $25.30   $25.30  
  7 purchase totals = $979.25       $1,078.1752   $1,078.18   $1,078.20   $1,078.20