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 $241.71   7.162%   $259.0213   $259.02   $259.00   $259.00  
  Purchase #2 $32.77   6.176%   $34.7939   $34.79   $34.80   $34.80  
  Purchase #3 $161.95   4.185%   $168.7276   $168.73   $168.75   $168.70  
  Purchase #4 $50.65   7.217%   $54.3054   $54.31   $54.30   $54.30  
  Purchase #5 $211.57   11.219%   $235.306   $235.31   $235.30   $235.30  
  Purchase #6 $200.98   4.499%   $210.0221   $210.02   $210.00   $210.00  
  Purchase #7 $59.94   9.112%   $65.4017   $65.40   $65.40   $65.40  
  7 purchase totals = $959.57       $1,027.5780   $1,027.58   $1,027.55   $1,027.50