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 $11.52   9.833%   $12.6528   $12.65   $12.65   $12.70  
  Purchase #2 $201.35   10.402%   $222.2944   $222.29   $222.30   $222.30  
  Purchase #3 $60.60   12.413%   $68.1223   $68.12   $68.10   $68.10  
  Purchase #4 $156.97   12.853%   $177.1454   $177.15   $177.15   $177.10  
  Purchase #5 $212.56   10.390%   $234.645   $234.65   $234.65   $234.60  
  Purchase #6 $203.98   6.214%   $216.6553   $216.66   $216.65   $216.70  
  Purchase #7 $242.28   8.264%   $262.302   $262.30   $262.30   $262.30  
  7 purchase totals = $1,089.26       $1,193.8172   $1,193.82   $1,193.80   $1,193.80