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 $248.67   6.232%   $264.1671   $264.17   $264.15   $264.20  
  Purchase #2 $168.29   7.560%   $181.0127   $181.01   $181.00   $181.00  
  Purchase #3 $78.43   10.530%   $86.6887   $86.69   $86.70   $86.70  
  Purchase #4 $125.84   9.317%   $137.5645   $137.56   $137.55   $137.60  
  Purchase #5 $153.32   10.679%   $169.693   $169.69   $169.70   $169.70  
  Purchase #6 $162.49   6.537%   $173.112   $173.11   $173.10   $173.10  
  Purchase #7 $22.98   13.565%   $26.0972   $26.10   $26.10   $26.10  
  7 purchase totals = $960.02       $1,038.3352   $1,038.33   $1,038.30   $1,038.40