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 $25.67   11.155%   $28.5335   $28.53   $28.55   $28.50  
  Purchase #2 $238.44   10.805%   $264.2034   $264.20   $264.20   $264.20  
  Purchase #3 $8.49   9.124%   $9.2646   $9.26   $9.25   $9.30  
  Purchase #4 $153.59   4.505%   $160.5092   $160.51   $160.50   $160.50  
  Purchase #5 $237.90   5.584%   $251.1843   $251.18   $251.20   $251.20  
  Purchase #6 $78.82   6.177%   $83.6887   $83.69   $83.70   $83.70  
  Purchase #7 $219.68   12.169%   $246.4129   $246.41   $246.40   $246.40  
  7 purchase totals = $962.59       $1,043.7966   $1,043.78   $1,043.80   $1,043.80