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 $195.65   13.639%   $222.3347   $222.33   $222.35   $222.30  
  Purchase #2 $116.37   12.672%   $131.1164   $131.12   $131.10   $131.10  
  Purchase #3 $44.30   8.263%   $47.9605   $47.96   $47.95   $48.00  
  Purchase #4 $202.75   8.256%   $219.489   $219.49   $219.50   $219.50  
  Purchase #5 $175.89   9.223%   $192.1123   $192.11   $192.10   $192.10  
  Purchase #6 $89.56   11.483%   $99.8442   $99.84   $99.85   $99.80  
  Purchase #7 $109.70   11.458%   $122.2694   $122.27   $122.25   $122.30  
  7 purchase totals = $934.22       $1,035.1265   $1,035.12   $1,035.10   $1,035.10