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 $244.44   5.620%   $258.1775   $258.18   $258.20   $258.20  
  Purchase #2 $6.82   11.192%   $7.5833   $7.58   $7.60   $7.60  
  Purchase #3 $37.81   3.201%   $39.0203   $39.02   $39.00   $39.00  
  Purchase #4 $237.53   7.267%   $254.7913   $254.79   $254.80   $254.80  
  Purchase #5 $195.77   4.536%   $204.6501   $204.65   $204.65   $204.70  
  Purchase #6 $169.37   3.313%   $174.9812   $174.98   $175.00   $175.00  
  Purchase #7 $203.77   9.466%   $223.0589   $223.06   $223.05   $223.10  
  7 purchase totals = $1,095.51       $1,162.2626   $1,162.26   $1,162.30   $1,162.40