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 $83.62   5.185%   $87.9557   $87.96   $87.95   $88.00  
  Purchase #2 $187.73   9.805%   $206.1369   $206.14   $206.15   $206.10  
  Purchase #3 $82.37   8.271%   $89.1828   $89.18   $89.20   $89.20  
  Purchase #4 $194.56   3.558%   $201.4824   $201.48   $201.50   $201.50  
  Purchase #5 $52.52   6.767%   $56.074   $56.07   $56.05   $56.10  
  Purchase #6 $98.35   12.161%   $110.3103   $110.31   $110.30   $110.30  
  Purchase #7 $41.85   7.327%   $44.9163   $44.92   $44.90   $44.90  
  7 purchase totals = $741.00       $796.0584   $796.06   $796.05   $796.10