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 $226.93   6.116%   $240.809   $240.81   $240.80   $240.80  
  Purchase #2 $224.85   7.346%   $241.3675   $241.37   $241.35   $241.40  
  Purchase #3 $49.41   7.430%   $53.0812   $53.08   $53.10   $53.10  
  Purchase #4 $87.78   10.194%   $96.7283   $96.73   $96.75   $96.70  
  Purchase #5 $74.42   7.608%   $80.0819   $80.08   $80.10   $80.10  
  Purchase #6 $153.39   8.306%   $166.1306   $166.13   $166.15   $166.10  
  Purchase #7 $203.69   3.301%   $210.4138   $210.41   $210.40   $210.40  
  7 purchase totals = $1,020.47       $1,088.6123   $1,088.61   $1,088.65   $1,088.60