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 $38.55   6.647%   $41.1124   $41.11   $41.10   $41.10  
  Purchase #2 $49.42   6.107%   $52.4381   $52.44   $52.45   $52.40  
  Purchase #3 $65.84   12.462%   $74.045   $74.05   $74.05   $74.00  
  Purchase #4 $147.69   11.121%   $164.1146   $164.11   $164.10   $164.10  
  Purchase #5 $175.92   4.371%   $183.6095   $183.61   $183.60   $183.60  
  Purchase #6 $211.59   9.704%   $232.1227   $232.12   $232.10   $232.10  
  Purchase #7 $250.72   9.549%   $274.6613   $274.66   $274.65   $274.70  
  7 purchase totals = $939.73       $1,022.1036   $1,022.10   $1,022.05   $1,022.00