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 $72.87   12.173%   $81.7405   $81.74   $81.75   $81.70  
  Purchase #2 $106.54   5.395%   $112.2878   $112.29   $112.30   $112.30  
  Purchase #3 $235.95   13.575%   $267.9802   $267.98   $268.00   $268.00  
  Purchase #4 $233.59   5.621%   $246.7201   $246.72   $246.70   $246.70  
  Purchase #5 $51.34   10.772%   $56.8703   $56.87   $56.85   $56.90  
  Purchase #6 $247.97   6.303%   $263.5995   $263.60   $263.60   $263.60  
  Purchase #7 $193.98   4.727%   $203.1494   $203.15   $203.15   $203.10  
  7 purchase totals = $1,142.24       $1,232.3478   $1,232.35   $1,232.35   $1,232.30