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 $61.62   7.713%   $66.3728   $66.37   $66.35   $66.40  
  Purchase #2 $200.73   5.779%   $212.3302   $212.33   $212.35   $212.30  
  Purchase #3 $164.82   11.745%   $184.1781   $184.18   $184.20   $184.20  
  Purchase #4 $245.58   11.179%   $273.0334   $273.03   $273.05   $273.00  
  Purchase #5 $31.73   8.132%   $34.3103   $34.31   $34.30   $34.30  
  Purchase #6 $86.45   8.530%   $93.8242   $93.82   $93.80   $93.80  
  Purchase #7 $141.91   6.459%   $151.076   $151.08   $151.10   $151.10  
  7 purchase totals = $932.84       $1,015.1250   $1,015.12   $1,015.15   $1,015.10