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 $243.93   11.241%   $271.3502   $271.35   $271.35   $271.40  
  Purchase #2 $212.96   13.185%   $241.0388   $241.04   $241.05   $241.00  
  Purchase #3 $107.82   8.675%   $117.1734   $117.17   $117.15   $117.20  
  Purchase #4 $44.29   4.831%   $46.4296   $46.43   $46.45   $46.40  
  Purchase #5 $224.95   9.656%   $246.6712   $246.67   $246.65   $246.70  
  Purchase #6 $184.89   3.695%   $191.7217   $191.72   $191.70   $191.70  
  Purchase #7 $78.37   13.837%   $89.2141   $89.21   $89.20   $89.20  
  7 purchase totals = $1,097.21       $1,203.5990   $1,203.59   $1,203.55   $1,203.60