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 $78.85   11.654%   $88.0392   $88.04   $88.05   $88.00  
  Purchase #2 $224.94   12.452%   $252.9495   $252.95   $252.95   $252.90  
  Purchase #3 $89.70   5.594%   $94.7178   $94.72   $94.70   $94.70  
  Purchase #4 $103.30   9.294%   $112.9007   $112.90   $112.90   $112.90  
  Purchase #5 $78.41   6.838%   $83.7717   $83.77   $83.75   $83.80  
  Purchase #6 $207.25   11.337%   $230.7459   $230.75   $230.75   $230.70  
  Purchase #7 $175.41   3.688%   $181.8791   $181.88   $181.90   $181.90  
  7 purchase totals = $957.86       $1,045.0039   $1,045.01   $1,045.00   $1,044.90