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 $203.88   8.240%   $220.6797   $220.68   $220.70   $220.70  
  Purchase #2 $211.82   4.271%   $220.8668   $220.87   $220.85   $220.90  
  Purchase #3 $117.91   6.772%   $125.8949   $125.89   $125.90   $125.90  
  Purchase #4 $24.35   3.646%   $25.2378   $25.24   $25.25   $25.20  
  Purchase #5 $159.52   13.661%   $181.312   $181.31   $181.30   $181.30  
  Purchase #6 $217.94   6.271%   $231.607   $231.61   $231.60   $231.60  
  Purchase #7 $133.82   8.502%   $145.1974   $145.20   $145.20   $145.20  
  7 purchase totals = $1,069.24       $1,150.7956   $1,150.80   $1,150.80   $1,150.80