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 $92.94   10.415%   $102.6197   $102.62   $102.60   $102.60  
  Purchase #2 $82.34   9.729%   $90.3509   $90.35   $90.35   $90.40  
  Purchase #3 $236.90   13.318%   $268.4503   $268.45   $268.45   $268.50  
  Purchase #4 $68.82   9.418%   $75.3015   $75.30   $75.30   $75.30  
  Purchase #5 $117.86   9.371%   $128.9047   $128.90   $128.90   $128.90  
  Purchase #6 $197.35   4.213%   $205.6644   $205.66   $205.65   $205.70  
  Purchase #7 $138.85   11.859%   $155.3162   $155.32   $155.30   $155.30  
  7 purchase totals = $935.06       $1,026.6077   $1,026.60   $1,026.55   $1,026.70