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 $65.57   6.141%   $69.5967   $69.60   $69.60   $69.60  
  Purchase #2 $188.43   12.310%   $211.6257   $211.63   $211.65   $211.60  
  Purchase #3 $167.66   12.231%   $188.1665   $188.17   $188.15   $188.20  
  Purchase #4 $152.87   11.642%   $170.6671   $170.67   $170.65   $170.70  
  Purchase #5 $245.77   4.342%   $256.4413   $256.44   $256.45   $256.40  
  Purchase #6 $229.41   10.161%   $252.7204   $252.72   $252.70   $252.70  
  Purchase #7 $152.92   10.731%   $169.3298   $169.33   $169.35   $169.30  
  7 purchase totals = $1,202.63       $1,318.5475   $1,318.56   $1,318.55   $1,318.50