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 $204.31   9.270%   $223.2495   $223.25   $223.25   $223.20  
  Purchase #2 $179.88   11.739%   $200.9961   $201.00   $201.00   $201.00  
  Purchase #3 $133.84   10.335%   $147.6724   $147.67   $147.65   $147.70  
  Purchase #4 $199.50   13.179%   $225.7921   $225.79   $225.80   $225.80  
  Purchase #5 $41.28   12.406%   $46.4012   $46.40   $46.40   $46.40  
  Purchase #6 $89.80   6.209%   $95.3757   $95.38   $95.40   $95.40  
  Purchase #7 $82.77   5.125%   $87.012   $87.01   $87.00   $87.00  
  7 purchase totals = $931.38       $1,026.4990   $1,026.50   $1,026.50   $1,026.50