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 $118.27   13.735%   $134.5144   $134.51   $134.50   $134.50  
  Purchase #2 $177.30   9.321%   $193.8261   $193.83   $193.85   $193.80  
  Purchase #3 $80.93   9.218%   $88.3901   $88.39   $88.40   $88.40  
  Purchase #4 $220.56   3.676%   $228.6678   $228.67   $228.65   $228.70  
  Purchase #5 $220.28   5.648%   $232.7214   $232.72   $232.70   $232.70  
  Purchase #6 $228.42   9.792%   $250.7869   $250.79   $250.80   $250.80  
  Purchase #7 $115.29   4.728%   $120.7409   $120.74   $120.75   $120.70  
  7 purchase totals = $1,161.05       $1,249.6476   $1,249.65   $1,249.65   $1,249.60