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 $181.98   5.717%   $192.3838   $192.38   $192.40   $192.40  
  Purchase #2 $174.59   12.693%   $196.7507   $196.75   $196.75   $196.80  
  Purchase #3 $141.41   5.615%   $149.3502   $149.35   $149.35   $149.40  
  Purchase #4 $58.58   5.592%   $61.8558   $61.86   $61.85   $61.90  
  Purchase #5 $202.92   6.464%   $216.0367   $216.04   $216.05   $216.00  
  Purchase #6 $158.85   4.415%   $165.8632   $165.86   $165.85   $165.90  
  Purchase #7 $26.35   3.554%   $27.2865   $27.29   $27.30   $27.30  
  7 purchase totals = $944.68       $1,009.5269   $1,009.53   $1,009.55   $1,009.70