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 $92.33   6.518%   $98.3481   $98.35   $98.35   $98.30  
  Purchase #2 $246.78   12.289%   $277.1068   $277.11   $277.10   $277.10  
  Purchase #3 $182.72   5.437%   $192.6545   $192.65   $192.65   $192.70  
  Purchase #4 $30.47   4.531%   $31.8506   $31.85   $31.85   $31.90  
  Purchase #5 $159.29   8.518%   $172.8583   $172.86   $172.85   $172.90  
  Purchase #6 $90.84   6.251%   $96.5184   $96.52   $96.50   $96.50  
  Purchase #7 $146.84   4.727%   $153.7811   $153.78   $153.80   $153.80  
  7 purchase totals = $949.27       $1,023.1178   $1,023.12   $1,023.10   $1,023.20