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 $119.85   11.529%   $133.6675   $133.67   $133.65   $133.70  
  Purchase #2 $194.86   9.488%   $213.3483   $213.35   $213.35   $213.30  
  Purchase #3 $21.88   4.400%   $22.8427   $22.84   $22.85   $22.80  
  Purchase #4 $214.43   6.601%   $228.5845   $228.58   $228.60   $228.60  
  Purchase #5 $204.44   3.415%   $211.4216   $211.42   $211.40   $211.40  
  Purchase #6 $211.54   12.806%   $238.6298   $238.63   $238.65   $238.60  
  Purchase #7 $53.32   12.156%   $59.8016   $59.80   $59.80   $59.80  
  7 purchase totals = $1,020.32       $1,108.2960   $1,108.29   $1,108.30   $1,108.20