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 $188.40   12.489%   $211.9293   $211.93   $211.95   $211.90  
  Purchase #2 $31.74   10.873%   $35.1911   $35.19   $35.20   $35.20  
  Purchase #3 $49.65   9.231%   $54.2332   $54.23   $54.25   $54.20  
  Purchase #4 $167.70   6.325%   $178.307   $178.31   $178.30   $178.30  
  Purchase #5 $245.33   11.830%   $274.3525   $274.35   $274.35   $274.40  
  Purchase #6 $202.60   13.803%   $230.5649   $230.56   $230.55   $230.60  
  Purchase #7 $232.25   7.807%   $250.3818   $250.38   $250.40   $250.40  
  7 purchase totals = $1,117.67       $1,234.9598   $1,234.95   $1,235.00   $1,235.00