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 $79.35   13.695%   $90.217   $90.22   $90.20   $90.20  
  Purchase #2 $174.55   12.674%   $196.6725   $196.67   $196.65   $196.70  
  Purchase #3 $191.56   10.137%   $210.9784   $210.98   $211.00   $211.00  
  Purchase #4 $158.32   7.245%   $169.7903   $169.79   $169.80   $169.80  
  Purchase #5 $123.80   10.850%   $137.2323   $137.23   $137.25   $137.20  
  Purchase #6 $48.62   8.720%   $52.8597   $52.86   $52.85   $52.90  
  Purchase #7 $178.87   12.404%   $201.057   $201.06   $201.05   $201.10  
  7 purchase totals = $955.07       $1,058.8072   $1,058.81   $1,058.80   $1,058.90