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 $32.65   13.522%   $37.0649   $37.06   $37.05   $37.10  
  Purchase #2 $157.94   10.415%   $174.3895   $174.39   $174.40   $174.40  
  Purchase #3 $201.40   8.867%   $219.2581   $219.26   $219.25   $219.30  
  Purchase #4 $246.69   9.386%   $269.8443   $269.84   $269.85   $269.80  
  Purchase #5 $31.82   13.186%   $36.0158   $36.02   $36.00   $36.00  
  Purchase #6 $116.99   7.800%   $126.1152   $126.12   $126.10   $126.10  
  Purchase #7 $192.56   12.162%   $215.9791   $215.98   $216.00   $216.00  
  7 purchase totals = $980.05       $1,078.6669   $1,078.67   $1,078.65   $1,078.70