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 $5.67   11.150%   $6.3022   $6.30   $6.30   $6.30  
  Purchase #2 $249.77   5.780%   $264.2067   $264.21   $264.20   $264.20  
  Purchase #3 $240.77   8.283%   $260.713   $260.71   $260.70   $260.70  
  Purchase #4 $54.84   11.424%   $61.1049   $61.10   $61.10   $61.10  
  Purchase #5 $212.51   13.482%   $241.1606   $241.16   $241.15   $241.20  
  Purchase #6 $76.38   6.118%   $81.0529   $81.05   $81.05   $81.10  
  Purchase #7 $216.46   10.408%   $238.9892   $238.99   $239.00   $239.00  
  7 purchase totals = $1,056.40       $1,153.5295   $1,153.52   $1,153.50   $1,153.60