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 $214.34   3.405%   $221.6383   $221.64   $221.65   $221.60  
  Purchase #2 $216.94   5.294%   $228.4248   $228.42   $228.40   $228.40  
  Purchase #3 $34.27   3.547%   $35.4856   $35.49   $35.50   $35.50  
  Purchase #4 $246.41   9.399%   $269.5701   $269.57   $269.55   $269.60  
  Purchase #5 $6.96   5.421%   $7.3373   $7.34   $7.35   $7.30  
  Purchase #6 $29.97   4.850%   $31.4235   $31.42   $31.40   $31.40  
  Purchase #7 $158.56   6.798%   $169.3389   $169.34   $169.35   $169.30  
  7 purchase totals = $907.45       $963.2185   $963.22   $963.20   $963.10