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 $248.81   10.570%   $275.1092   $275.11   $275.10   $275.10  
  Purchase #2 $107.44   13.849%   $122.3194   $122.32   $122.30   $122.30  
  Purchase #3 $248.63   4.294%   $259.3062   $259.31   $259.30   $259.30  
  Purchase #4 $238.95   11.142%   $265.5738   $265.57   $265.55   $265.60  
  Purchase #5 $9.77   9.694%   $10.7171   $10.72   $10.70   $10.70  
  Purchase #6 $86.36   4.698%   $90.4172   $90.42   $90.40   $90.40  
  Purchase #7 $181.40   13.251%   $205.4373   $205.44   $205.45   $205.40  
  7 purchase totals = $1,121.36       $1,228.8802   $1,228.89   $1,228.80   $1,228.80