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 $193.80   5.623%   $204.6974   $204.70   $204.70   $204.70  
  Purchase #2 $98.34   4.208%   $102.4781   $102.48   $102.50   $102.50  
  Purchase #3 $188.65   5.672%   $199.3502   $199.35   $199.35   $199.40  
  Purchase #4 $165.68   13.349%   $187.7966   $187.80   $187.80   $187.80  
  Purchase #5 $149.77   10.699%   $165.7939   $165.79   $165.80   $165.80  
  Purchase #6 $50.56   12.485%   $56.8724   $56.87   $56.85   $56.90  
  Purchase #7 $88.52   3.513%   $91.6297   $91.63   $91.65   $91.60  
  7 purchase totals = $935.32       $1,008.6183   $1,008.62   $1,008.65   $1,008.70