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 $184.40   10.604%   $203.9538   $203.95   $203.95   $204.00  
  Purchase #2 $247.94   6.551%   $264.1825   $264.18   $264.20   $264.20  
  Purchase #3 $226.83   10.626%   $250.933   $250.93   $250.95   $250.90  
  Purchase #4 $43.38   10.299%   $47.8477   $47.85   $47.85   $47.80  
  Purchase #5 $211.70   9.336%   $231.4643   $231.46   $231.45   $231.50  
  Purchase #6 $8.43   12.645%   $9.496   $9.50   $9.50   $9.50  
  Purchase #7 $141.53   5.508%   $149.3255   $149.33   $149.35   $149.30  
  7 purchase totals = $1,064.21       $1,157.2028   $1,157.20   $1,157.25   $1,157.20