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 $70.25   5.514%   $74.1236   $74.12   $74.10   $74.10  
  Purchase #2 $174.84   9.436%   $191.3379   $191.34   $191.35   $191.30  
  Purchase #3 $244.67   9.121%   $266.9864   $266.99   $267.00   $267.00  
  Purchase #4 $205.87   6.354%   $218.951   $218.95   $218.95   $219.00  
  Purchase #5 $78.96   11.326%   $87.903   $87.90   $87.90   $87.90  
  Purchase #6 $175.36   4.790%   $183.7597   $183.76   $183.75   $183.80  
  Purchase #7 $10.30   5.292%   $10.8451   $10.85   $10.85   $10.80  
  7 purchase totals = $960.25       $1,033.9067   $1,033.91   $1,033.90   $1,033.90