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 $202.84   10.842%   $224.8319   $224.83   $224.85   $224.80  
  Purchase #2 $118.96   6.511%   $126.7055   $126.71   $126.70   $126.70  
  Purchase #3 $214.76   4.866%   $225.2102   $225.21   $225.20   $225.20  
  Purchase #4 $8.85   5.174%   $9.3079   $9.31   $9.30   $9.30  
  Purchase #5 $201.38   9.215%   $219.9372   $219.94   $219.95   $219.90  
  Purchase #6 $184.74   10.852%   $204.788   $204.79   $204.80   $204.80  
  Purchase #7 $67.86   5.232%   $71.4104   $71.41   $71.40   $71.40  
  7 purchase totals = $999.39       $1,082.1911   $1,082.20   $1,082.20   $1,082.10