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 $23.35   12.215%   $26.2022   $26.20   $26.20   $26.20  
  Purchase #2 $250.80   9.385%   $274.3376   $274.34   $274.35   $274.30  
  Purchase #3 $41.64   9.700%   $45.6791   $45.68   $45.70   $45.70  
  Purchase #4 $132.83   11.405%   $147.9793   $147.98   $148.00   $148.00  
  Purchase #5 $30.91   4.475%   $32.2932   $32.29   $32.30   $32.30  
  Purchase #6 $211.98   11.207%   $235.7366   $235.74   $235.75   $235.70  
  Purchase #7 $245.41   12.681%   $276.5304   $276.53   $276.55   $276.50  
  7 purchase totals = $936.92       $1,038.7584   $1,038.76   $1,038.85   $1,038.70