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 $247.75   8.436%   $268.6502   $268.65   $268.65   $268.70  
  Purchase #2 $181.88   11.349%   $202.5216   $202.52   $202.50   $202.50  
  Purchase #3 $119.90   4.689%   $125.5221   $125.52   $125.50   $125.50  
  Purchase #4 $197.35   4.244%   $205.7255   $205.73   $205.75   $205.70  
  Purchase #5 $131.58   10.743%   $145.7156   $145.72   $145.70   $145.70  
  Purchase #6 $184.54   12.462%   $207.5374   $207.54   $207.55   $207.50  
  Purchase #7 $45.79   3.411%   $47.3519   $47.35   $47.35   $47.40  
  7 purchase totals = $1,108.79       $1,203.0243   $1,203.03   $1,203.00   $1,203.00