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 $23.80   9.674%   $26.1024   $26.10   $26.10   $26.10  
  Purchase #2 $19.34   6.167%   $20.5327   $20.53   $20.55   $20.50  
  Purchase #3 $202.25   10.592%   $223.6723   $223.67   $223.65   $223.70  
  Purchase #4 $212.60   6.815%   $227.0887   $227.09   $227.10   $227.10  
  Purchase #5 $63.40   9.669%   $69.5301   $69.53   $69.55   $69.50  
  Purchase #6 $121.73   4.767%   $127.5329   $127.53   $127.55   $127.50  
  Purchase #7 $59.87   9.500%   $65.5577   $65.56   $65.55   $65.60  
  7 purchase totals = $702.99       $760.0168   $760.01   $760.05   $760.00